The Guardian reportedÂ on its Web site that Newton had posted a message on hisÂ Facebookprofile early Sunday saying, "Luv U all but it's end time."

The United Kingdom Anti-Doping Agency suspended Newton for two years in February after a blood sample he had provided as part of an out-of-competition drug test showed he had been using H.G.H. After the positive test was announced, he admitted to using the substance.

In June, Newton, who was considered a very talented player, said that the positive test had initially not bothered him. But since the rugby season had started, he said, the suspension had begun "to sink in."

"I've made one of the biggest mistakes of my life, and I know it is something I will regret for the rest of my life," he said.

News of the positive test quickly reverberated throughout the world of sports, appearing to validate the blood test for sports officials in Major League Baseball. The officials had been skeptical of the test, which had been used since 2004 mostly to test Olympic athletes by the World Anti-Doping Agency but which had delivered no positive tests.

CommissionerÂ Bud SeligÂ and his drug-testing officials immediately began putting together plans to start the blood test in the minor leagues, where Selig could act without the consent of the players union. In July,Â Selig instituted H.G.H. testing in the minor leagues, the first time a pro league in North America committed to testing blood for performance-enhancing drugs.

Newton last played for the Wakefield Trinity Wildcats in the Super League, a 14-team grouping that plays a style known as rugby league. That style is a more physical and wide-open game than the more international and popular rugby union.Â